Intramedullary threaded nail for radial cortical fixation

ABSTRACT

The present invention relates to a device and system for fixation of intra-articular and extra-articular fractures and non-unions of small bones and other small bone fragments, and more particularly to a threaded nail with a robust length and a trailing end with a cutting tip and longitudinal cutting flutes and a stepped diameter with cutting flutes at the transition point, and an optional cannulation along the central longitudinal axis of the nail.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.

This application is a divisional of U.S. patent application Ser. No.16/805,485, filed Feb. 28, 2020, entitled INTRAMEDULLARY THREADED NAILFOR RADIAL CORTICAL FIXATION, which is a continuation of InternationalPatent Application No. PCT/US2018/049342, filed Sep. 4, 2018, entitledINTRAMEDULLARY THREADED NAIL FOR RADIAL CORTICAL FIXATION, which claimsthe benefit of priority to U.S. Provisional Patent Application No.62/554,123, filed Sep. 5, 2017, entitled INTRAMEDULLARY THREADED NAIL,the entirety of which is hereby incorporated by reference herein andshould be considered part of this specification.

FIELD OF THE INVENTION

The present invention relates to a device and system for fixation offractures and non-unions of small bones and other small bone fragments,and more particularly to a threaded nail with a robust length and aheadless leading end with a torque driving recess and a trailing endwith a cutting tip and longitudinal cutting flutes, and an intermediatestepped diameter with cutting flutes at the transition point,Optionally, the device includes a cannulation along the centrallongitudinal axis of the nail. This intramedullary nail provides forfull shaft-length and internally circumferential cortical fixation inparticular for use in the metacarpals and metatarsals. Thus, the implantachieves at least a frictional fit circumferentially with the internalcortex for at least 60% +/−15% of the intramedullary canal length bymeans of engagement with a penetrating supplemental spiral thread alongat least 80% +/−15% of the length of the implant.

BACKGROUND OF THE INVENTION

Trauma to the mid-hand and mid-foot can have life-changing effects forthe victim as a result of loss of function, disfiguration, and even thelengthy and onerous treatment protocols. It's hard and sometimesimpossible to do without the use of a foot or hand, and in particular,when one is living “hand to mouth”.

Current methods of treatment include internal fixation with surgery,like plating systems and wire fixation or in the case of non-displacedfractures, casting the hand or foot without surgical intervention. Thesetreatments involve a substantial period, i.e., several weeks or months,in which the injured hand or foot is immobilized. However, seriousproblems with adhesions, loss of muscle, proprioception and nervehealth, can result from dis-use for these periods of time. Moreover,beyond the side effects of the treatment protocol, there are problemswith compliance and with the issues of daily living that result from notbeing able to use a hand or foot for these prolonged periods of time.

While it is possible for hand and foot accidents to occur during variousactivities, including traffic accidents, firearm mis-fire, and extremesport activities, there is a greater correlation of the risk for suchtraumatic events in manual and low wage jobs. Thus, the incidence andthe effects of such accidents are skewed to jobs on the lower end of thepay-scale and may often involve workers who are already at economicrisk. Thus, victims of hand or foot trauma will often either resort tonon-compliance involving the early use of the injured limb, or in someinstances will suffer the loss of income, including the loss of a jobaltogether, which sets off a spiraling decline in the ability to “makeends meet”, expanding the risk from the injury to the loss of house andhome and family stability.

Finally, it should be noted that the hand is paramount to every aspectof our humanity and is instrumental in dictating and defining ourrelationship to our world. Injury to the hand hinders that relationshipand our perception of our role in that world, especially in cases wherethe hand is disfigured, or appears to be disabled. Our hands areconstantly in view to ourselves and to the world, and debilitating scarsor irregularities such as scars, and even the Frankenstein-like outlinesof surgical hardware on the mid-hand, are visible and painful remindersof a traumatic event and its aftermath.

The prior art orthopedic implants for use in small bones in the arms andlegs have a set of criteria that differs from those of the long bonesand large joints. These bones, (generally in the elbow and below and theknee and below), tend to be smaller in diameter and present a differingratio of cortical to cancellous bone, as well as the issues of coveringsoft tissue and a relatively large nexus of tendons, ligaments andnerves, to complicate surgical techniques. The present invention isintended to answer these issues, and to provide a solution to surgicalfixation of broken or fractured small bones through a threaded nailintended for intramedullary fixation and most importantly, allowing aswift return to daily living, and reduced disability, pain, andrehabilitation.

One typical small bone implant location is the hand or foot, and inparticular in the metacarpals and metatarsals. The structure of the handis composed of the scaphoid and other carpal bones which meet with theradius and the ulna at the wrist joint, the metacarpals, and phalanges.The back of the hand includes the metacarpals, and a metacarpal connectseach finger and thumb to the hand, while the fingers and thumb areformed of bones called phalanges. The connection of the phalanges to themetacarpals is called a “knuckle” joint or metacarpophalangeal joint(MCP joint), and acts like a hinge when the fingers or thumb are bent.In each finger, there are three phalanges that are separated by twojoints called the interphalangeal joints (IP joints). The proximal IPjoint (PIP joint) is the one closest to the MCP joint. The other jointclosest to the end of the finger is the distal IP joint (DIP joint). Thethumb just has one IP joint. The joints are covered on the ends witharticular cartilage. The foot has an analogous structure, with the talusinterfacing between the tibia and the fibula on the leg, and thecalcaneus on the foot, and the mid-foot being comprised of the tarsals,including the cuneiforms, (i.e., the cuboid and the navicular bones,)the metatarsals, and the phalanges.

Damage to these bones of the extremities may occur as a result of asprain or fracture or trauma and typically following reduction tore-align a damaged bone, it should be stabilized in position to allow itto heal in that position.

In the past, a surgical procedure to stabilize these broken bones hasinvolved drilling a pilot hole and insertion of a k-wire or smooth nailalong the length of the bone to hold it in position while the boneheals. An opening is first formed in the metacarpal bone, wherein theopening extends through the fracture and the nail is positioned bywedging it in the opening through the soft cancellous intermediate boneso that the nail provides stability for the parts of the bone on eitherside of the fracture. After a certain period, a second surgery isrequired to remove the nail from the bone. Problems with this procedureare that, because it is not anchored in the bone and in fact, mostlyinterfaces with the spongy central bone pulp, it can migrate through themetacarpal bone and into surrounding tissue. Sometimes this can resultin damage to soft tissue, such as a severed or damaged tendon orcartilage, and/or cause pain. Another problem with the nail is that,because it can migrate, a second surgery is required to remove it.Additionally, the proximal end of pins and nails can cause tendonirritation, tendon rupture or skin irritation and infection.

One theoretical solution to this problem is to insert a screw into thebone however, the torque required to place a screw into the length of ametacarpal bone (which is a relatively thin, delicate but brittle bone)is high. Such a procedure would be lengthy, and there would be apossibility of bone damage, or damage to the driving head of the screw,which could prevent complete insertion into the opening formed in thebone. Current screws are not designed specifically for intramedullaryplacement. For instance, the current screws are frequently not longenough, nor do they account for the narrowed waist of the metacarpal ormetatarsal bones.

Thus, the present invention is intended for fixation of intra-articularand extra-articular fractures and non-unions of small bones and smallbone fragments; including for example, arthrodesis of small joints;bunionectomies and osteotomies, including scaphoid and other carpalsbones, metacarpals, tarsals, metatarsals, patella, ulnar, styloid,capitellum, radial head and radial styloid, and is preferably intendedfor intramedullary fixation of metacarpal and phalangeal fractures toprovide surgeons with a reliable solution through a simple approach. Therobust length offering, (more than 3.5 centimeters, and preferably morethan 4 centimeters, or 5 centimeters +/−1 or 0.5 centimeters, or even upto 7.5 centimeters), with large length to diameter ratio (more than15:1, and preferably more than 20:1), and with a differential diameter(having a leading length at a smaller diameter of 3-5 mm, and a trailinglength towards the nail head, of from 0.4-2 mm smaller, with goodexamples of 3.2/3.6 or 4.0/4.5), accurately fits native metacarpal andphalangeal locations to create a strong, stable fixation and precisereduction. Moreover, the invention is intended to fill theintramedullary canal along substantially all its length (i.e., more that45%, or preferably more than 50%, and preferably more than 60%, or 70%and up to 80% or 98% by length). The design includes a leading, meaningaway from the nail end, section having a smaller outer diameter of theroot and also of the thread crest at that section, but a relativelyconstant internal cannulation where the leading section is from 40-60%of the length. The larger diameter section reinforces the area next tothe torque receiving end of the nail so that the greater material allowstransmission of the torque through the device, and the cutting flutes inthe transition section between the dual diameters helps to keep thesmaller leading portion from collapsing on itself. Thus, the device isdesigned to allow both insertion and removal by screwing or unscrewingthe implant into the intramedullary canal.

In addition, the invention is unique as it is designed to captureinternal cortical bone so that not only does the nail extend asubstantial distance of the length of the shaft (at least 60% includingpenetration past the isthmus), it also is used so that is achieves“radial” or “circumferential” fixation within the canal, and preferably,achieves 360° internal circumferential cortical fixation. This is novelfor the metacarpal application since the metacarpals (and metatarsals)include a narrowed waist area, the “isthmus” of the metacarpal (andmetatarsals). Past screws and intramedullary implants are not designedto engage with sufficient length or to grab the internal walls of thecanal circumferentially over substantial distance of the length, but thecurrent design includes a stepped diameter with a leading cutting tipand an intermediate cutting feature that allows the invention to reamthe canal to size as it is advanced through the canal. Thus, the canalis prepped for circumferential cortical fixation, which is unique to thepresent invention and refers to the use of an implant that includes asurface that is fixed to the internal cortical wall or of theintramedullary shaft, in particular of the metacarpal of the metatarsal.The nail is intended to avoid applying a compressive force along thelength of the nail, and can be used in instances in which there is avoid in the bone or missing bone fragments and nail stabilizes theremaining bone fragments with a gap to restore the length of themetacarpal. The nail is dual diameter with both leading-diameter andtrailing-diameter sections substantially cylindrical and, importantly,not tapered or conical to permit the device to maintain contact with thehole in the canal during removal and to ease removal by unscrewing thenail.

The present invention can be used in a procedure that lets the patientreturn to work in a short period of time, from two weeks to the nextday, including jobs ranging from manual labor, care-giver, professionalmusician, artist, and professional athlete. This return to functionalliving, and the decrease in down-time, and rehabilitation and risk todaily living is a huge societal saving.

SUMMARY OF THE INVENTION

The present invention solves the problems associated with repairing ametacarpal or metatarsal fracture or dislocation by providing a devicethat is a unique combination of a nail and a screw, which can beinserted into the bone without damaging the bone because it is sized andshaped to achieve circumferential intramedullary cortical fixation andto support the bone from the inside, (even when there's a bone gap offrom 0 up to 2, 2.5, or even 3 cm along the length of a damagedmetacarpal), to fit the narrowed portion of these bones by providing atleast one stepped diameter and a fluted transition between thediameters, by providing a headless design with a uniform lead(s) whichavoids compression and which can be seated below the surface of the boneto avoid the irritation that can result from a proud portion; byproviding for a cannulated surgical technique with an intramedullaryimplant designed to minimize soft tissue, cartilage and vascular damageupon insertion; and to facilitate early, active mobilizationpost-operative protocols for accelerated healing and earlier return towork.

Further, as the device achieves radial internal fixation, the device issecured within the bone, which eliminates migration and eliminates theneed for a second operation to remove the device. Thus, the deviceprovides a cannulated cylindrical core having an outer exterior surfacealong its length, (from 35 to 75, or even as long as lengths to 120 or130 mm) that defines an inner diameter (minor diameter) relative to thelateral edge of a threaded portion which defines an outer diameter(major diameter). The design includes one or more stepped portion whichallow for an increase in the trailing portion of at least the outerdiameter or the inner diameter, and more preferably of both the outerdiameter and the inner diameter. The transition area also includeslongitudinal cutting flutes (2-5 of 3 to 10 mm length) to account forthis increase at a length of the nail (i.e., from 25% to 75%, andpreferably 35% to 60%, of the distance of the length from the trailingend) which allows a clearance of the narrowed or “waisted” portion ofthe bone. The cannulation is generally a constant diameter (for ease ofmanufacture) through the length of the nail, but could include a dualdiameter which might include an over grind at the larger diameter ortrailing end of the nail which includes the torque driving feature, suchas an internal or external hexagon or hexalobe configuration.

The device includes a leading portion that has 2-5 cutting teeth on thebeveled leading tip, and along the long side, also includes additionallongitudinal flutes, which, as are the other flutes, intended to providefor reaming away of the cancellous intramedullary material and forscoring of the inner surface of the intramedullary channel, as well as aplace for additional cancellous material to reside during surgery.

The thread defined between the outer diameter and the inner diameter cansuitably include a right handed single start thread with a pitch of from3 to 5 mm, and preferably at least 4.0 mm+/−0.25, or a dual lead threadof the same lead value and a pitch value half of the lead value with asecondary thread having a lower height, i.e., from 40% to 75% or 50%+/−5% of the height of the primary thread. The leading and followingflanks of the threads together form an angle of 5° to 60°, andpreferably 15°±10°, and are connected by a thread crest of length 0.05to 0.2 mm which is separated from the root diameter by a thread depth of0.2 mm to 0.8 mm.

At its first end, or trailing end, the device includes a driving recesscapable of being driven by a suitable driver into the opening, such as ahexalobe or a T10 drive recess, to generate significant torque to biteinto the cortical bone and avoid harm to the lower material narrowerleading end of the nail.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top side view of a device in accordance with the invention;

FIG. 2 is a side view of the device of FIG. 1;

FIG. 3 is a cross-section of the device of FIG. 1 taken along line A.-A;

FIG. 4 is a detail of FIG. 3 showing the thread characteristics and adetail of the thread shape;

FIG. 5 is an end view of the proximal view of the device of FIG. 1;

FIG. 6 is an end view of the distal tip of the device of FIG. 1;

FIG. 7 is a side view detail of the transition section of the blank fromwhich the invention is made and showing the intermediate cutting flutesof FIG. 1;

FIG. 8 is a side view detail of the distal end of the blank from whichthe invention is made and showing the distal cutting flutes of FIG. 1;

FIG. 9 is a top view of a skeleton of a hand showing the implant of theinvention in place in a fractured metacarpal;

FIG. 10 is an illustration of the step of measuring a metacarpal for usewith a technique in accordance' with the invention;

FIG. 11 is an illustration of the step of inserting a guide wire in aretrograde fashion to anatomically reduce the fracture fragments inaccordance with the technique of the invention;

FIG. 12 is an illustration of the entry point of the guide wire of FIG.11 in the dorsal third of the metacarpal head;

FIG. 13 is an illustration of the step of drilling by passing acannulated drill over the guide wire;

FIG. 14 is an illustration of the step of inserting the implant in themetacarpal in accordance with the surgical technique of the invention;

FIG. 15. is a side view of a second embodiment of the device of FIG. 1;

FIG. 16 is a cross-section of the device of FIG. 15 taken along lineC-C;

FIG. 17 is a detail of FIG. 16 showing the thread characteristics and adetail of the thread shape;

FIG. 18 is a side view of the blank from which the invention is made andshowing the transition section, the intermediate cutting flutes anddistal cutting flutes of FIG. 15;

FIG. 19 is an end view of the proximal view of the device of FIG. 15;and

FIG. 20 is an end view of the distal tip of the device of FIG. 15.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an exemplary embodiment 1 o of the threaded intramedullarynail of the present invention. The nail 1 O may be formed of anysuitable biocompatible material, such as surgical grade stainless steel,titanium, alloys of nickel and chromium, nitinol, PEEK, hydroxyapatite,bio-glass or other bio compatible materials or combinations of thesematerials. The nail 1 O has a first end, or proximal end, 12, a secondend, or distal end, 14, a shaft 16 with an outer surface 17, and acenter portion 18 between first end 12 and second end 14. A cutting end19 with a bevel and two, three or four teeth 19a is provided at thetrailing end 14 (which is distal relative to the torque driving recessbut is implanted in the proximal portion of the metacarpal) and adriving surface 20 in a drive recess 22 is formed in the top of firstend 12.

The cutting point 19 helps to cut through any bone left behind when thebone is drilled to receive device 1 O, and further include 2-5 equallyradially spaced longitudinal cutting flutes 23 which extend lengthwisein the exterior surface and through the threads of the nail 10. Thedriving surface 20 in this embodiment has a hexalobe driveconfiguration, although any suitable driving configuration may be used.Other driving configurations that may be used include slotted, Pozidriv,Robertson, tri-wing, Torq-Set, Spanner flead, Triple Square and hexhead.

Extending length wise in outer surface 17, preferably along thelongitudinal axis of shaft 16, are grooves or cutting flutes 24. As usedherein, “extending length wise” means that each groove 24 is elongatedand extends along the shaft with one end of the groove nearer the firstend 12 and the opposite end of the groove nearer the second end 14, butgrooves 24 may be formed at an angle and not necessarily formed alongthe longitudinal axis shaft 16, although that is preferred. Grooves 24preferably have edges that assist in boring the device 1 0 into andanchoring device 1 O in the opening in a bone. Grooves 24 also maycapture some debris left behind from the bone drilling process to createthe opening created when device 1 0 is positioned into the opening.

The shaft 18 of the nail 1 O of the present invention includes at leasttwo sections of differing diameters, for example, a proximal sectionthat extends for a length of from about 15% to 30% of the length of thedevice, and which is located at from 25% to 75%, and preferably at55-65% of the distance of the length from the distal end of the device10. Further, the device provides a cannulated cylindrical core or shaft18 having an outer exterior surface 17 along its length, (which isprovided in 5 mm increments from 35 to 75 mm) that defines an innerdiameter relative to the lateral edge of a threaded portion whichdefines an outer diameter. The design includes one or more steppedportion which allow for a 0.25-1.0 mm increase in the proximal portionof at least the outer diameter or the inner diameter, and morepreferably of both the outer diameter and the inner diameter. Thetransition area also includes longitudinal cutting flutes (2-5 of 3 to 10 mm length) to account for this increase at a length of the nail (i.e.,from 25% to 75%, and preferably from 50% to 60%, of the distance of thelength from the proximal end) which allows a clearance of the narrowedor “waisted” portion of the bone.

The device includes a thread 25 which is defined between the outerdiameter and the inner diameter and can suitably include a right-handedsingle start thread with a pitch of from 3 to 5 mm, and preferably atleast 4.0+/−0.25 mm with a similar lead value. Alternatively, as isshown in FIGS. 15, 16 and 17, the device may include a double leadthread 125 having a first thread 126 and a second thread 127 of the samelead value with the second thread 127 having a height that isapproximately 50% of the height of the first thread 126.

The leading and following flanks of the threads together form an angleof 5° to 60°, and preferably 15±10°, and are connected by a thread crestof length 0.05 to 0.2 mm which is separated from the root diameter by athread depth of 0.2 mm to 0.8 mm.

FIG. 9 illustrates a nail 1 0 in accordance with the present inventionin position in a fourth metacarpal and securing a reduced fracture.

In FIG. 10, in a first step of a surgical technique in accordance withthe invention, the size of the metacarpal 30 at issue is determined inorder to size the implant.

In FIG. 11, it is illustrated that the fracture in the bone is alignedand then a guide wire 32 is inserted in the intramedullary canal inretrograde.

FIG. 12 illustrates the optimal position 34 for the insertion of theguide wire.

In FIG. 13 a cannulated drill 33, uses the guide wire as a guide todrill an opening into the metacarpal bone which extends through thefracture and provides enough space on each side of the fracture toproperly position device 1 0.

In FIG. 14, the device 1 0 is driven into the opening in the metacarpalbone by means of the drive recess. The outer diameter of the threads 28,is slightly larger than the inner diameter of the opening in the bone.This provides bone material for threads 28 to thread into and provides atight fit for device 10.

Having thus described some embodiments of the invention, othervariations and embodiments that do not depart from the spirit of theinvention will become apparent to those skilled in the art. The scope ofthe present invention is thus not limited to any particular embodiment,but is instead set forth in the appended claims and the legalequivalents thereof. Unless expressly stated in the written descriptionor claims, the steps of any method recited in the claims may beperformed in any order capable of yielding the desired result.

What is claimed is:
 1. A method of fixation of a bone having anintramedullary canal about an axis and a head and which is a metacarpalor a metatarsal, the method comprising: surgically exposing the bone;forming a hole in the bone extending along the axis to expose a canalhaving an internal surface of cortical bone; inserting a guide wire inthe hole; placing an implant having a cannulation over the guide wireand screwing the implant into the hole in the bone, the implant furtherincluding a first end with a first external diameter and a second endwith a second external diameter and a transition portion between thefirst end and the second end, the transition portion including at leastone cutting flute and the second end including at least one cuttingflute, and the first end including a torque driving feature, the implanthaving a thread on a first section nearer to the first end and on asecond section nearer to the second end, whereby the thread of theimplant fixes the implant to the internal surface of the cortical bone.2. A method of fixation as set forth in claim 1 wherein the bone is ametacarpal and the implant extends through the isthmus of themetacarpal.
 3. A method of fixation as set forth in claim 1 wherein thefirst section has a constant first minor diameter along a first lengthand the second section has a constant second minor diameter along asecond length.
 4. A method of fixation as set forth in claim 2 whereinthe first length is more than 40% of the second length.
 5. A method offixation as set forth in claim 3 wherein the first length is more than50% of the second length.
 6. A method of fixation as set forth in claim1 wherein the thread of the first threaded section has the same pitch asthe thread of the second threaded section.
 7. A method of fixation asset forth in claim 1 wherein the thread of the first threaded section iscontiguous the thread of the second threaded section.
 8. A method offixation as set forth in claim 1 wherein the intermediate transitioncomprises a taper and the at least one cutting flute intersects thetaper.
 9. A method of fixation as set forth in claim 1 wherein thethreads of the first and second threaded sections are each double leadthreads.
 10. A method of fixation as set forth in claim 9 wherein thedouble lead threads comprise a first threads having a first pitch valueand second threads having a second pitch value, and the first pitchvalue and the second pitch value are the same.
 11. A method of fixationas set forth in claim 10 wherein the thread of the first section has afirst thread height and the thread of the second section has a secondthread height and the second thread height is less than the first threadheight.